Differential Diagnosis: Hyponatremia

Following are differential diagnoses for patients presented with decreased blood sodium level.

Normal osmolality (290-310 mOsm/kg) 

• Pseudohyponatremia (eg, hypertriglyceridemia, hyperproteinemia) 

Low osmolality (<290 mOsm/kg)

• Polyuric renal failure

• GI fluid loss (eg, vomiting, diarrhea, regurgitation, severe ileus with “pooled” insensible fluid losses) 

• Hookworm infection

• Severe dietary sodium restriction

• Iatrogenic (eg, hypotonic fluids, diuretics)

• Third-space loss 

  • Pancreatitis

  • Peritonitis

  • Pleural or peritoneal effusion

  • Uroabdomen

• Hypoadrenocorticism

• Edematous disorders 

  • Congestive heart failure

  • Liver failure

  • Nephrotic syndrome

• Syndrome of inappropriate antidiuretic hormone secretion  

• Psychogenic polydipsia

High osmolality (>310 mOsm/kg)

• Diabetes mellitus (ie, secondary to hyperglycemia) 

• Iatrogenic (ie, mannitol administration)